1. Field of the Invention
The invention relates to a vehicle control apparatus that controls the operation of a vehicle engine and an electric power steering (EPS) device.
2. Description of the Related Art
An EPS device using a motor as a drive source has been conventionally used as a power steering device for a vehicle, and because such as a device has a large number of advantages, such as a high degree of layout freedom and small energy consumption, the use thereof has recently expanded to a wide range of vehicle types.
A power source (battery) of such an EPS also serves as a power source of a cell motor that is used for cranking when the engine is started. As a result, the application of an assist force with the EPS has conventionally been stopped when the cranking was performed.
Thus, where the EPS is actuated when the power source voltage is lowered in the course of cranking, an excessive current can be taken out from the battery. A state in which such an excessive service current is generated can be assumed to occur, for example, during abrupt steering or during the maximum steering angle is maintained. As a result, the following problem is encountered: the battery is overdischarged and a state is assumed in which the engine cannot be restarted or a drive circuit or the like is damaged by the inflow of such an excessive current. Accordingly, in order to avoid the occurrence of these problems, the application of assist force with the EPS is stopped in advance when cranking is performed.
However, in recent years, in order to reduce the amount of exhaust gas, the number of vehicles provided with the so-called idling stop function, which causes the engine to stop automatically when the vehicle is stopped, has increased, and in such a vehicle, cranking has to be frequently performed to restart the stopped engine. Furthermore, since the number of events in which the cranking is performed simultaneously with a steering operation increases accordingly, the interruption and re-application of an assist force that occur because the EPS is stopped during cranking create an uncomfortable latent feel in steering.
According to, for example, Japanese Patent Application Publication No. 2005-271640 (JP-A-2005-271640), when the engine is stopped and a steering wheel is operated by a small amount, the power assist control by EPS is continued with a limited motor output. On the other hand, when the engine is stopped and the steering wheel is operated by the large amount, the power assist control is stopped till the engine is restarted. Furthermore, according to Japanese Patent Application Publication No. 2006-151335 (JP-A-2006-151335), when an engine stop is detected, the revolution speed of the EPS drive motor is gradually reduced, and when an engine restart is detected, the revolution speed is gradually increased. By limiting the motor output as described above, the power assist control during cranking is performed, while inhibiting the occurrence of the aforementioned excessive service current, and degradation of the steering feel in this process can be suppressed.
However, although the use of the above-described conventional features results in significant improvement, where these reductions of the motor output are implemented rapidly to obtain the effect quickly, the resultant fluctuations of assist force can degrade the steering feel. Therefore, it is preferred that the reduction of motor output be implemented gradually, but in this case, the possibility of the excessive service current occurring in this process rises, and in this respect there still remains some space for improvement.